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At least 595 records · Page 33Linked to original sources
PubMed1997

The adaptational system as a dynamical feedback system.

The characteristics of biological systems of adaptation are developed from the principle that the manifestations of life are modified by and must conform with their environment in order to enable organismic persistence. The two roles of the environment, termed "modifying" and "adaptive", give rise to the distinction of three elementary and sequentially coupled subsystems characterizing the adaptational system: the modifying system, comparator system, and state regulation system. The third system determines which state alterations are required for adaptation of manifestations (responses) to the demands of the adaptive environment. Adaptational valuation is introduced as a measure of adaptedness of response to adaptive environment. The dynamical aspect of adaptation is shown to be completely described by the timing of feedback. Discrete and continuous forms of adaptation can thus be treated on the same conceptional basis. All steps of the generic system formulation are illustrated with the help of a simple model with additive effects and linear state regulation. The system representation is used to demonstrate how basic intuitive conceptions, such as adaptational lag or adaptational capacity, can be made amenable to precise analysis. Another demonstration concerns recognition of adaptational clues resulting from the distinction between the two environmental classes, modifying and adaptive. Among these clues are challenges of low correlation between the two classes to adaptational systems and the specification of questions of the evolution of phenotypic plasticity.

Adaptation, Biological↗
PubMed1978

Host-phage relationships in the genus Mycobacterium and their clinical significance.

Progress made during the last 15 years in the studies on the relationships between mycobacteria and their bacteriophages is reviewed. The basic biology of the phages and the applications of studies on adaptation and host range are discussed in relation to the development of phage typing systems for epidemiological purposes. The nature of lysogeny, its natural occurrence, its experimental establishment, the effect of the lysogenic state on the host bacterium and the evidence that lysogenic mycobacteria are involved in human disease, especially sarcoidosis, is reviewed.

Adaptation, Biological↗
PubMed2003

Natural history of Homo erectus.

Our view of H. erectus is vastly different today than when Pithecanthropus erectus was described in 1894. Since its synonimization into Homo, views of the species and its distribution have varied from a single, widely dispersed, polytypic species ultimately ancestral to all later Homo, to a derived, regional isolate ultimately marginal to later hominin evolution. A revised chronostratigraphic framework and recent work bearing either directly or indirectly on reconstructions of life-history patterns are reviewed here and, together with a review of the cranial and postcranial anatomy of H. erectus, are used to generate a natural history of the species. Here I argue that H. erectus is a hominin, notable for its increased body size, that originates in the latest Pliocene/earliest Pleistocene of Africa and quickly disperses into Western and Eastern Asia. It is also an increasingly derived hominin with several regional morphs sustained by intermittent isolation, particularly in Southeast Asia. This view differs from several current views, most especially that which recognizes only a single hominin species in the Pleistocene, H. sapiens, and those which would atomize H. erectus into a multiplicity of taxa. Following Jolly ([2001] Yrbk Phys Anthropol 44:177-204), the regional morphs of H. erectus may be productively viewed as geographically replacing allotaxa, rather than as the focus of unresolvable species debates. Such a view allows us to focus on the adaptations and biology of local groups, including questions of biogeographic isolation and local adaptation. A number of issues remain unresolved, including the significance of diversity in size and shape in the early African and Georgian records.

Adolescent↗
PubMed1999

Homoplasy, homology and the problem of 'sameness' in biology.

The reality of evolution requires some concept of 'sameness'. That which evolves changes its state to some degree, however minute or grand, although parts remain 'the same'. Yet homology, our word for sameness, while universal in the sense of being necessarily true, can only ever be partial with respect to features that change. Determining what is equivalent to what among taxa, and from what something has evolved, remain real problems, but the word homology is not helpful in these problematic contexts. Henning saw this clearly when he coined new terms with technical meanings for phylogenetic studies. Analysis in phylogenetic systematics remains contentious and relatively subjective, especially as new information accumulates or as one changes one's mind about characters. This pragmatic decision making should not be called homology assessment. Homology as a concept anticipated evolution. Homology dates to pre-evolutionary times and represents late 18th and early 19th century idealism. Our attempts to recycle words in science leads to difficulty, and we should eschew giving precise modern definitions to terms that originally arose in entirely different contexts. Rather than continue to refine our homology concept we should focus on issues that have high relevance to modern evolutionary biology, in particular homoplasy--derived similarity--whose biological bases require elucidation.

Adaptation, Biological↗
PubMed1986

Biological characteristics of a cold-adapted influenza A virus mutation residing on a polymerase gene.

The biological function of a cold-adapted (ca) mutation residing on the PB2 gene of an influenza A/Ann Arbor/6/60 (A/AA/6/60) ca variant virus in the viral replication cycle at 25 degrees C was studied. The viral polypeptide synthesis of A/AA/6/60 ca variant at 25 degrees C was evident approximately 6 hours earlier than the wild type (wt) virus and yielded twice as many products. The quantitative analysis of viral complementary RNA (cRNA), synthesized in the presence of cycloheximide, revealed that A/AA/6/60 ca variant and a single gene reassortant that contains only the PB2 gene of the ca variant with remaining genes of the wt virus produced equal amount of cRNA at 25 degrees and 33 degrees C, which was an amount approximately four fold greater than the wt virus' cRNA synthesized at 25 degrees C. These results strongly suggest that the ca mutation residing on the PB2 gene of A/AA/6/60 ca variant affects the messenger RNA synthesis at 25 degrees C in the primary transcription.

Cold Temperature↗
PubMed2006

Adaptation aftereffects in the perception of gender from biological motion.

Human visual perception is highly adaptive. While this has been known and studied for a long time in domains such as color vision, motion perception, or the processing of spatial frequency, a number of more recent studies have shown that adaptation and adaptation aftereffects also occur in high-level visual domains like shape perception and face recognition. Here, we present data that demonstrate a pronounced aftereffect in response to adaptation to the perceived gender of biological motion point-light walkers. A walker that is perceived to be ambiguous in gender under neutral adaptation appears to be male after adaptation with an exaggerated female walker and female after adaptation with an exaggerated male walker. We discuss this adaptation aftereffect as a tool to characterize and probe the mechanisms underlying biological motion perception.

Adaptation, Physiological↗
PubMed1996

Adaptation: a new concept in radiation biology and oncology and its clinical relevance.

A new concept of adaptation and cross-resistance in radiation biology and oncology is introduced. It explains the apparent difference in the radiosensitivity of cells of the same type (both normal and tumor) that are located in different parts of the body. Oxygen tension, which varies considerably from one part of the human body to another, ranges from 20 mmHg to 159 mmHg (2.7-21%). When cells are adapted to live in areas with high physiologic oxygen tension (high normoxic) such as the epidermis and upper and lower airways, they develop better antioxidant mechanisms, which include free radical scavengers and DNA repair, than cells that live in lower physiologic oxygen tension (low normoxic). Because the mechanisms of cell-damaging effects of ionizing radiation are similar to those of oxygen, the cell that is resistant to oxygen toxicity also becomes resistant to ionizing radiation (and certain cancer chemotherapeutic agents). Based on this concept, it could be expected that some human tumors such as primary cutaneous malignant melanoma and lung cancers contain cells that are relatively resistant to ionizing radiation as a consequence of living in a high normoxic condition and the treatment of these tumors may require different strategies.

Adaptation, Physiological↗
PubMed1994

Cytogenetic adaptive response with multiple small X-ray doses in mouse germ cells and its biological influence on the offspring of adapted males.

Cytogenetic adaptive response of mouse germ cells was studied by exposing male mice to a sequence of 4 conditioning doses of 0.05 Gy each (D1) administered at 10-day intervals and subsequently to a single challenging dose of 1.5 Gy (D2). In concurrent experiments, male mice after treatment with D1 doses alone were mated to unirradiated females and the F1 males were given the D2 dose. Chromosomal aberrations in both spermatocytes and bone-marrow cells and UV-induced UDS in splenocytes of these mice were studied. Adapted mice (i.e., D1 + D2 exposures) responded with a significantly lower frequency of chromosomal aberrations than the non-adapted (D2 exposure only) controls. The relative reduction in frequencies was, however, similar to that observed in earlier work with a single conditioning dose of 0.05 Gy. The frequencies of chromosomal aberrations in spermatocytes and bone-marrow cells as well as the levels of UV-induced UDS in splenocytes of the F1 males in the group D1 to fathers + D2 to F1 males were the same as those in F1 males which received only the D2 exposure.

Adaptation, Physiological↗